Cannabis Use Damages the Lungs in a Different Way to Tobacco, Study Finds
Smoking cannabis regularly can damage the lungs in a different way to smoking tobacco, according to a new cohort study published in the American Journal of Respiratory and Critical Care Medicine.
In the study, both tobacco and cannabis smokers had higher static lung scores, indicative of overinflated lungs, but the cannabis smokers had, on average, higher lung volumes and lower rates of gas transfer.
The researchers behind the study have thus warned that regular cannabis smokers are at risk of lung complications, especially if they also smoke tobacco.
Inhale, exhale
To get their results, the researchers at the University of Otago studied data from a decades-long ongoing study in New Zealand.
The Dunedin Multidisciplinary Health and Development Study has followed the lives of 1,037 people born between April 1972 and March 1973 at Queen Mary Maternity Hospital, Dunedin. Throughout this time, the participants have had their lungs tested and cannabis use documented; about 75 percent of the participants admit to using cannabis at some point in their lives.
As such, the Dunedin Study may have the world’s most complete data on lifetime cannabis use and lung function in a large population sample, according to Robert Hancox, a professor of preventive and social medicine at the University of Otago and lead author of the study.
Hancox and his colleagues compared the lung function test scores of the Dunedin participants when they were aged 45.
They found that both the cannabis smokers and the tobacco smokers had significantly low FEV1/FVC ratios, which is the ratio of the forced volume of an exhale in the first second to the forced vital capacity of the lungs.
For cannabis smokers, this low FEV1/FVC ratio was largely due to their high FVC scores (the total amount of air exhaled during the breathing test). While for the tobacco smokers, the low ratio was mostly due to their low FEV1 scores (the amount of air exhaled in the first breath).
Both tobacco and cannabis smokers had higher static lung scores, indicative of overinflated lungs, but the cannabis smokers had, on average, higher lung volumes and lower rates of gas transfer.
“As far as we are aware, this is the first time that a reduction in gas transfer has been reported in association with cannabis use, with previous cross-sectional studies finding no association,” the researchers wrote in their study.
“It is likely that [...] other studies did not follow cannabis users for long enough to demonstrate an impairment of gas transfer.”
According to the researchers, their findings indicate that long-term cannabis use could lead to problems similar to emphysema, a lung disease that causes shortness of breath through the slow destruction of lung tissue.
“Although emphysema does not appear to be common among cannabis users unless they also smoke tobacco, there are numerous reports of giant bullous emphysema among heavy cannabis users suggesting that long term cannabis may lead to alveolar destruction,” they wrote in their paper.
As to why the lungs of cannabis and tobacco smokers appeared to differ, the researchers are unsure, but posit that the different smoking habits associated with the two substances could be to blame.
“Cannabis users tend to smoke far fewer times a day than tobacco smokers and it is possible that the participants have not smoked enough cannabis for it to have a measurable effect on some aspects of lung function,” they wrote.
While the study has its limitations – there were no data on how much cannabis the participants used or how it was consumed – the authors say their findings can still help inform global debates on cannabis legalization.
“In some countries, there has been little discussion about the potential respiratory health consequences of increased cannabis consumption,” they wrote.
“Interpreting the evidence in the context of forming policies presents difficulties however: it is increasingly clear that cannabis has different effects on lung function to tobacco and the effects of widespread cannabis use will not necessarily mirror the harms caused by tobacco smoking.”
Cannabis and the lungs
Prior studies comparing the effects of cannabis and tobacco smoke have also found differing outcomes, and not always in marijuana’s favor.
Last year, research from the Ottawa Hospital, Canada, found that cannabis smokers experience emphysema at higher rates than both non-smokers and tobacco smokers.
After looking at CT scans of the lungs of patients, the researchers observed that rates of emphysema were significantly higher in the cannabis-using group; 75 percent of the scans of these patients showed signs of emphysema, compared to just 5 percent of control patients.
Another recent study from researchers at the University of Michigan found that teens who vape cannabis are almost twice as likely to report problems with wheezing and coughing than their peers who use tobacco cigarettes or vape nicotine products.
Lung cancers, on the other hand, appear to have a null association with cannabis use, despite the presence of carcinogens in cannabis smoke. As for the reasons behind this null effect, one scientific review published in 2015 posited that cannabinoids like THC counteract the carcinogens with their known tumor-suppressant effects.
